In declaring the Trinity to be a mystery that we cannot fully understand, we are seeing it as a truth which, although we cannot fully understand, is not completely beyond understanding. It is a truth that is not altogether beyond our understanding.
No, we should apply our feeble powers toward understanding the Trinity as far as we can. To that end I like thinking of the Trinity in two ways.
First in likening it to a mystery of three persons, I like recalling ancient Greek plays in which a single actor would wear three different masks through which he spoke ( per sona).
Secondly, I feel I can approach some understanding of the mystery that is both simple and complex by applying to it the saying of Dante, "All things among themselves an order, and this order is the form that makes the universe like God."